Most efficient way to pipe web beacon logs to Apache Flume?

Most efficient way to pipe web beacon logs to Apache Flume?

The Setup
I've setup a simple Nginx server that logs (in a JSON) format, which is
then piped to an S3 bucket with Apache Flume. All the Nginx server does is
respond with a web beacon tracking pixel and write to the log file.
Everything's cool so far.
The Problem
However, it would be nice to handle a couple other processing steps at
this level of the pipeline:
Convert query string parameters into actual JSON in the event records
Set a UUID cookie for tracking purposes
Increment some counters in a local database (eventually all the data will
be processed with a Map/Reduce)
It seems like I'll need a custom Flume sink to convert the query string
parameters and a backend to nginx to set the cookie and update the
database. It seems very inefficient to have several systems in play here,
especially when optimizing throughput for hundreds of requests per second.
Possible Solutions
My first thought was to use NodeJS, which could handle all these tasks
(and even replace nginx?), but I don't like that it's single-threaded
(maybe spawn child workers?).
Then I thought maybe the processing should happen at the Flume agent
level, and a Java program could handle everything (any performance
advantage here due to Flume's being written in Java?)
Questions
Am I going about this the right way, or overthinking it?
How would you recommend consolidating everything into one or two processes?